At 3rd level, you master the art of the ambush. You can give yourself a bonus to your initiative rolls equal to your Wisdom modifier.

And the Tactical Wit class feature of the wizard War Mage archetype (XGtE, pg. 60):

Starting at 2nd level, your keen ability to assess tactical situations allows you to act quickly in battle. You can give yourself a bonus to your initiative rolls equal to your Intelligence modifier.

So, a level 6 character who was a Ranger 4/Wizard 2 who took the Alert feat at level 4 would have an initiative bonus of 5 + DEX + WIS + INT.

So, if my Ranger 4/Wizard 2 example above made it all the way up to level 20 (Ranger 18/Wizard 2) and used all their ASIs to max out DEX, INT and WIS, they would then have an initiative bonus of 20.

What character build (up to level 20 if necessary) gives the maximum initiative bonus?

Or, is the one I have outlined here the highest you can get?

For the purposes of this, let's assume the PC is a human (+1 to all ability scores) whose player was lucky enough to roll all 17s during character creation; hence the character has +4 in every stat (for convenience). Anything RAW is allowed; multiclassing, feats, magic items, etc, but nothing from Unearthed Arcana. No temporary effects. Things that grant advantage or half-proficiency count, but nothing temporary.

If we are taking a super lucky human why stop at rolling 17 for all stats? Why not 18?
– SdjzDec 3 at 16:48

@Sdjz The "17s in all stats and human with +1 to all" was to elimitate racial bonuses to stats to make this question simpler. I basically wanted a "plain" PC with 18s in all stats and no further complications.
– NathanSDec 3 at 17:10

1

Based on John Carroll's comment, it may be better to remove your attempt at the "highest" and add it as an answer. THat will simplify and clarify the question.
– NautArchDec 3 at 18:02

1

@NathanS the most recent edit should remove the ambiguity that John saw. I didn't really have any confusion about what you meant in the original wording, but I think that should address it regardless. I don't think removing the build you have is necessary.
– RubiksmooseDec 3 at 18:08

1

@SirTechSpec "gain a bonus" doesn't imply choice, but "you can give" does. If for any reason it is beneficial for you to drop farther back in initiative order (independent mount, synergy with other players), you can choose to forego that bonus to bring your initiative where you want it.
– The Great JavaDec 6 at 4:53

5 Answers
5

I'm going to disregard any DM sanity here, and assume anything and everything published is on the table...

Attributes - +10

+10 from any attribute, because there are shenanigans that will allow you to get them to 30 involving combinations of attribute-increasing tome/manuals, Deck of Many Things Star cards, etc.

Base bonus is therefore +10 from Dexterity.

Class - +33, +43 total

The starting 18s across the board allow for unlimited multi-classing, so we won't have any problems getting the build off the ground before we go hunting for shenanigans. You'll probably want to start with Fighter for the Heavy Armor Proficiency, because there's a solid bonus available only on a suit of Plate.

+3 (at L20) Champion Fighter1 7 from Remarkable Athlete, because Initiative is a Dexterity check.2 We could use (Any) Bard 2 for Jack of All Trades, depending on what magic item we pick below, but we want that Heavy Armor profiency, so Fighter is the best choice.

Feats - +5, +48 total

At some point, one of the classes needs to be taken to L4 to earn an ASI for:

Equipment - +8 minimum, possibly infinite.

Right off the bat we can get +5 from Scorpion Armor1. It might be better to be a Yuan-Ti, because Scorpion Armor tries to kill the wearer via poison damage each time they take it off or put it on.

A Stone of Good Luck gives another +1 to all ability checks, while the Ioun Stone of Mastery increases the character's proficiency bonus by 1, which benefits Remarkable Athlete. We can use one or the other, because we've got an attunement slot limit.

While we're talking items, you'll want something like a Sentinel Shield to grant advantage on initiative - the Weapon of Warning or Rod of Alertness are out because we are using our last attunement slot to embrace absurdity: add another +1d10 from the Sword of Kas, a sentient evil artifact sword.

Guardian. The item whispers warnings to its bearer, granting a +2 bonus to initiative if the bearer isn’t incapacitated.

Let's say our particular Ioun Stone or Stone of Good Luck has it. Beyond that, it is ultimately up to the DM if other items with these properties show up.

The existence of this property means there is no theoretical ceiling - it doesn't have to be on attunement-required items. I know of at least two that exist in Adventures League play - a hand crossbow and a shield - and there may be more. There is the question of stacking effects, too. Is the Guardian property on two items the "same source"? That's up to the DM to decide.

Grand Total - +56+1d10... or more.

If we restrict the stats to more "normal" ranges, say 20s (for +5), it only drops to +36. No matter how you slice it, if you deliberately build a character with the express intent to "go first every time", you can overwhelm the variable d20 with static bonuses. Of course, the character may not have anything worth doing when they go first, and after the first round it doesn't really matter all that much.

1If half-proficiency is acquired via Bard, there's room for Barbarian 7 for built-in advantage on Initiative from Feral Instinct, but you either wouldn't have Heavy Armor Proficiency to wear the Scorpion Plate, or you'd have to burn a feat for it.

2Both abilities here specify "that doesn’t already use your proficiency bonus". If you interpret using half the bonus doesn't count as "already us[ing] your proficiency bonus", then you could have both for another +3.

Comments are not for extended discussion; this conversation has been moved to chat.
– mxyzplk♦Dec 4 at 2:52

1

Don't forget to ask if you can use the UA variant ranger for those few levels so you can get advantage on your checks!
– ExalDec 4 at 7:28

Its not infinite. You cant benefit from an effect with the same name more than once. DMG Errata Chapter 8 Combining Game Effects (p. 252). "But when two or more game features have the same name, only the effects of one of them—the most potent one—apply while the durations of the effects overlap." rpg.stackexchange.com/a/114946/41253
– ChrisDec 4 at 16:01

@Chris That point is already addressed in the answer, and explicitly left as a matter for DM discretion.
– T.J.L.Dec 4 at 18:19

@T.J.L. The quote answers that question. You cant have two effects with the same name. It doesn't matter that they're two different items our sources.
– ChrisDec 4 at 21:55

1We use Fighter 7 instead of Bard 2 for Jack of all Trades to have the option to use the Ioun Stone of Mastery as Remarkable Athlete rounds up while Jack of all Trades rounds down. If you are using Luckstone, you can go Bard 2 instead and just replace Any 2 with Any 7 (as long as you pick up the Alert feat from somewhere)

The Gear

A Tome of Understanding

A Tome of Clear Thought

A Tome of Leadership and Influence

A Manual of Quickness of Action

A suit of Scorpion Armor

The Sword of Kas

An Ioun Stone of Mastery or a Luckstone (with the Guardian minor property)

The Reading

Each of the Tomes and Manuals are used to increase your Dexterity, Intelligence, Wisdom, and Charisma to godlike levels. However, they only increase your ability scores in increments of +2 and then...

The manual ... loses its magic, but regains it in a century.

The best way to wait out a century is with the help of Sphinx lair actions, so Cindy simply asks Sven for help. Then Sven, after you spend a month reading each of the books, alters...

the flow of time within the lair ... such that everything within moves up to 10 years forward or backward (sphinx’s choice).

After doing this ten times, the books regain their magic and you can go back 100 years to read again. Do this until the relevant ability scores are at 30 (for a +10 ability modifier). Then just protect the lair for a century with Sven to make sure the books don't get stolen during their "incubation".

The Calculation

Below is the final calculation for the Initiative bonus:

Base: +10 [Total so far]

When combat starts, every participant makes a Dexterity check to determine their place in the initiative order.

Dread Ambusher: +10 [+20]

You can give yourself a bonus to your initiative rolls equal to your Wisdom modifier.

Rakish Audacity: +10 [+30]

You can give yourself a bonus to your initiative rolls equal to your Charisma modifier.

Tactical Wit: +10 [+40]

You can give yourself a bonus to your initiative rolls equal to your Intelligence modifier.

Remarkable Athlete: +3 [+43]

you can add half your proficiency bonus (round up) to any ... Dexterity ... check you make that doesn’t already use your proficiency bonus.

Alert: +5 [+48]

You gain a +5 bonus to initiative

Scorpion Armor: +5 [+53]

+5 bonus to initiative as long as you aren't incapacitated

The Sword of Kas: +1d10 [+53 +1d10]

you add a d10 to your initiative at the start of every combat

Luckstone

you gain a +1 bonus to ability checks

or Ioun Stone of Mastery: +1 [+54 +1d10]

Your proficiency bonus increases by 1

The Ioun Stone works by improving the bonus granted by Remarkable Athlete to +4

Guardian: +2 [+56 + 1d10]

+2 bonus to initiative if the bearer isn’t incapacitated.

And there we have it. Cindy is the fastest gun in the west.

Advantage?

If using the Bard 2/Luckstone build, your Any 7 could be in Barbarian to get Feral Instinct:

you have advantage on initiative rolls.

Otherwise, you will need to pick up a Sentinel Shield for the same effect.

+28 to initiative roll without items, 32-35 with.

What character build (up to level 20 if necessary) gives the maximum
initiative bonus? Or, is the one I have outlined here the highest you
can get? For the purposes of this, let's assume the PC is a human
(+1 to all ability scores) whose player was lucky enough to roll all
17s during character creation; hence the character has +4 in every
stat (for convenience).

Starting from all 18's (human, 17's +1) the initiative bonuses from all but Strength and Constitution accrue this way:

With items:

Any +2 boost to Int, Cha, Wis, Dex: +1 per item, or per suitable tome / book read.

Books, very rare. But if you get one each of Wisdom, Dex, Cha, Int,
your initiative boost is 32. Manual of Quickness of Action (Dex +2), Tome of Clear (Int +2) Tome of Understanding (Wis +2) Tome of leadership and influence (Cha +2)

If you took Fighter at level 1, you have + 7 to all saving throws, but + 10 to Strength and Constitution saving throws. Nice side effect.

Epic Boons

A boost of +2 to any of those stats (Dex, Int, Wis, Cha) via an epic boon (DMG) is another +1 per such boon.
It is possible that a raw boost to initiative of + {something} is offered as an epic boon, though were it my PC, I'd rather get anything else as an epic boon.

Well at that point your initiative is +20, so you have a 50% chance of rolling a 30 or higher. No monster or other player is going be be able to beat that.

Disclaimer I'm going to assume this guy has a 20 in Wis Dex Cha and Int.

A minimum initiative of 22 (not considering a natural 1 but I'll get to that) is going to be hard to beat.
But there are ways to make it even better.

Fist
Take at least three levels of rogue and get swashbuckler. Now you can add Charisma to your initiative. Then take a couple levels in bard and pick up jack of all trades.

Then you need 5 magic items

No.1
Manual of Quickness of Action Now your Dex bonus is +6.

No.2
Tome of Clear Thought now your Intelligence is +6.

No.3
Tome of understanding, now your Wisdom is +6.

No.4
Tome of leadership and influence, now your Charisma Is +6

No.5
The rod of alertness which gives you advantage on initiative rolls

Which brings to the lovely bonus of +31 6+6+6+6+5+2. And you roll with advantage.

Now with that roll your minimum becomes 33, With a maximum of 51. But what if you roll a natural 1, Well play a halfling, I pretty sure you can reroll initiative with lucky which means no natural 1s for you.
Then you get the luck feat, so now you can reroll 3 d20s. So if you roll a 2 (Very difficult with advantage) and get a measly 33 you can reroll. So you basically have triple advantage and and can reroll 1s.

And even if you have the minimum stats for every class. 13 Dex 13 Int and 13 Wis and with a 13 in Cha. Your bonuses are a +5 to base, + 2 with Dex, Cha, Wis, and Int. At this point your level 10 so + 2 with jack of all trades.

Which will be +15 bring your minimum Initiative to 15 and your max to 25. Which is still ridiculously good!

That's everything I can think of, granted I only have the core books and the SCAG so my information is rather limited. Hope this helps!